Repetitive strain disorders associated with prolonged use of keyboards, particularly computer keyboards, are a rapidly growing problem. Chronic musculoskeletal disorders such as carpal tunnel syndrome, muscle pain syndromes, wrist tenosynovitis, and epicondylitis have been linked to prolonged use of computer keyboards. Injuries to the hands, wrists and arms are associated with prolonged, repetitive, and excessively forceful typing. These injuries result in pain and disability, declining employee morale and productivity, and increased medical compensation costs.
Therefore, there is a need for a device that will help to prevent repetitive strain disorders among users of computer keyboards.
To date, the keyboard industry has focused on re-designing the shape of the standard keyboard. However, as there are many keyboards presently in use, to re-design and replace these keyboards would be extremely costly.
A recent study has shown that typical keyboard users exert 2.5 to 5 times more force than is necessary to activate the keys on the keyboard. These users often "bottom out" the keys on every keystroke. One writer observes that the force exerted at the tip of the thumb is magnified tenfold as it acts upon the basal joint at the wrist, and another speculates that the force exerted at the fingertips may be amplified by a factor of 2 to 4 as it acts upon the flexor tendons of the fingers.
In sum, computer users strike the keys with excessive force, and this force may act upon the tendons, joints and other structures of the fingers, wrist and arm with potentially destructive force. This contributes to the high incidence of musculoskeletal disorders among computer keyboard users.
Another study by Michael Feuerstein, Tom Armstrong and Paul Hickey, "Keyboard Force, Fatigue and Pain in Symptomatic and Asymptomatic Wordprocessors", 12th Congress of the International Ergonomics Association, confirmed that professional word processors type 4-5 times harder than necessary. The researchers also found that among workers with symptoms of repetitive strain, the ones with the most severe symptoms strike the keys significantly harder than those with minimal symptoms. Furthermore, the workers with the highest typing force tend to minimize their symptoms and the impact of their symptoms on their functioning. The authors speculate that this may create a "high risk" condition for increased frequency, severity and/or duration of injury.
A study by David Rempel and Jack Gerson, "Fingertip Forces While Using Three Different Keyboards", Proceedings of Human Factors Society, 35th Annual Meeting, 1991, concludes that high fingertip forces may contribute to the development of chronic musculoskeletal disorders, and that a relatively minor reduction in applied fingertip force will significantly reduce the daily cumulative force applied by the fingers.
It is common practice among medical professionals to advise keyboard users who suffer from repetitive strain disorders to use less force in activating the keys. However, it is well known that most users cannot comply with this advice, especially under stressful workplace conditions with deadlines, productivity quotas, etc.
Therefore, there is a need for a device that will assist computer keyboard users to strike the keys with less force and interrupt their patterns of repetitive movement. In particular, there is a need for a device that can be used with any existing keyboard and personal computer, including those already installed and in use, and that is low in cost and simple for the average user to install and operate.
Ergonomic studies have used various techniques to measure the force with which a user's fingers strike one or more keys on the keyboard. For example, Rempel, Dennerlein, Mote and Armstrong describe in "Fingertip Impact Loading During Keyboard Use", Proceedings of NACOB II, The Second North American Congress on Biomechanics, Chicago, 1992, pp. 425-456, a method to measure fingertip force during a keystroke using a piezoelectric load cell mounted in a keycap. The keyboard of this study was instrumented to measure vertical fingertip force applied by a finger during a typical typing task. The study by Rempel and Gerson (cited above) used a strain gauge load cell to measure and collect peak fingertip force. A study by Dennerlein, Serina, Mote and Rempel, reported in "Fingertip Kinematics And Forces During Typing", American Society of Biomechanics, 17th Annual Meeting, 1993, used a quarter bridge strain gauge load cell placed above the keyswitch and below the keycap of the "f" key to measure vertical fingertip impact force. In this study, the bridge signal was amplified and filtered before being sampled by an A/D board in the computer. A study titled "Fingertip Force Histories From Multiple Keys During Typing" by Smutz, Dennerlein, Mote and Rempel, American Society of Biomechanics, 17th Annual Meeting, 1993, instrumented multiple keys of a standard keyboard to collect fingertips' force histories.
These studies have used devices to measure and record fingertip force for scientific evaluation. In particular, these studies require that one or more keys of the keyboard be modified so as to include an instrument to measure force when the modified key(s) is used. Moreover, these devices, apart from being costly to produce, do not provide real-time feedback to a user of the keyboard as the user actually types.
There is need for a simple-to-install system to determine fingertip force in real-time when a keyboard is being used by a user and to interactively (in real time) alert the user if the user is striking the keys too hard, thus interrupting the cycle of repetitive typing motion.